// ==++==
// 
//   Copyright (c) Microsoft Corporation.  All rights reserved.
// 
// ==--==
// <OWNER>Microsoft</OWNER>
// 

using System;

namespace System.Collections {
    public static class StructuralComparisons {

        private static volatile IComparer s_StructuralComparer;
        private static volatile IEqualityComparer s_StructuralEqualityComparer;

        public static IComparer StructuralComparer {
            get {
                IComparer comparer = s_StructuralComparer;
                if (comparer == null) {
                    comparer = new StructuralComparer();
                    s_StructuralComparer = comparer;
                }
                return comparer;
            }
        }

        public static IEqualityComparer StructuralEqualityComparer {
            get {
                IEqualityComparer comparer = s_StructuralEqualityComparer;
                if (comparer == null) {
                    comparer = new StructuralEqualityComparer();
                    s_StructuralEqualityComparer = comparer;
                }
                return comparer;
            }
        }
    }

    [Serializable]
    internal class StructuralEqualityComparer : IEqualityComparer {
        public new bool Equals(Object x, Object y) {
            if (x != null) {

                IStructuralEquatable seObj = x as IStructuralEquatable;

                if (seObj != null){
                    return seObj.Equals(y, this);
                }

                if (y != null) {
                    return x.Equals(y);
                } else {
                    return false;
                }
            }
            if (y != null) return false;
            return true;
        }

        public int GetHashCode(Object obj) {
            if (obj == null) return 0;

            IStructuralEquatable seObj = obj as IStructuralEquatable;

            if (seObj != null) {
                return seObj.GetHashCode(this);
            }

            return obj.GetHashCode();
        }
    }

    [Serializable]
    internal class StructuralComparer : IComparer {
        public int Compare(Object x, Object y) {

            if (x == null) return y == null ? 0 : -1;
            if (y == null) return 1;

            IStructuralComparable scX = x as IStructuralComparable;

            if (scX != null) {
                return scX.CompareTo(y, this);
            }

            return Comparer.Default.Compare(x, y);
        }
    }        

}
